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(Circulation. 2002;105:54.)
© 2002 American Heart Association, Inc.

Clinical Investigation and Reports

Gas Exchange Detection of Exercise-Induced Right-to-Left Shunt in Patients With Primary Pulmonary Hypertension

Xing-Guo Sun, MD; James E. Hansen, MD; Ronald J. Oudiz, MD; Karlman Wasserman, MD, PhD

From the Department of Medicine, Harbor-UCLA Medical Center, Torrance, Calif.

Correspondence to Karlman Wasserman, MD, PhD, the Department of Medicine, Harbor-UCLA Medical Center, Torrance, CA 90509-2910. E-mail kwasserm{at}ucla.edu

Background— Because of high pulmonary vascular resistance in patients with primary pulmonary hypertension (PPH), right atrial pressure may exceed left atrial pressure during exercise, resulting in a right-to-left shunt via a patent foramen ovale (PFO). This shunting would disturb arterial PCO₂ and H⁺ homeostasis if the pulmonary blood were not simultaneously hyperventilated to compensate for the high CO₂ and H⁺ in the shunted blood. This article first hypothesizes and then describes unique changes in gas exchange when right-to-left exercise-induced shunting (EIS) occurs.

Methods and Results— Retrospectively, the cardiopulmonary exercise tests of 71 PPH patients were studied. Criteria postulated to document hyperventilation of the pulmonary blood flow due to a right-to-left EIS were (1) an abrupt and sustained increase in end-tidal O₂ with a simultaneous sustained decrease in end-tidal CO₂; (2) an abrupt and sustained increase in the respiratory exchange ratio; and (3) usually, an associated decline in pulse oximetry saturation. Each patient was evaluated for a PFO with resting echocardiography. The investigators interpreting the gas exchange evidence of EIS were blinded to the echocardiographic readings. Forty-five percent of the patients had demonstrable EIS by gas exchange criteria. Almost all were also positive for a PFO by echocardiography. Using the resting echocardiograph as the reference, the sensitivity, specificity, positive and negative predictive values, and accuracy were all between 90% to 96%.

Conclusions— Exercise-induced right-to-left shunting can be detected by noninvasive, cardiopulmonary exercise testing in patients with PPH.

Key Words: shunts • echocardiography • exercise • hypertension, pulmonary

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